Setting an object to a random position in the BGE
The problem is that your script controller is on the Enemy Dropper object and attempts to reference mySensor which does not exist on that object. If you check the console, accessed by Window > Toggle System Console (only on windows systems), you will see an error.


  Traceback (most recent call last):
    File "Setting Position.py", line 9, in 
  KeyError: 'value = gameOb[key]: KX_GameObject, key "mySensor" does not exist'
  Python script error - object 'Enemy Dropper', controller 'Python':


To make it operable, add the mySensor sensor to the Enemy Dropper object's logic bricks.